A poppet valve may be used in an internal combustion engine to control the flow of a fuel/air mixture from a fuel intake port of a cylinder head into a combustion chamber of the engine. The poppet valve circumferentially seals the valve face and a valve seat. When the valve is closed, the valve face is pressed tightly against the valve seat insert and the fuel/air mixture is blocked by the valve. When the valve is open, the valve face is disengaged from the valve seat and the fuel/air mixture may flow through the valve.
In a cast iron cylinder head, the valve seat may be integral to the cylinder head, but in an aluminum or aluminum alloy cylinder head, the valve seat insert may be inserted into a cylinder head seat pocket. A valve seat insert may be made of a sintered metal alloy which is harder and more wear resistant than aluminum. The valve seat insert is typically press-fitted into the cylinder head seat pocket and a small gap may remain between the valve seat insert and the back of the cylinder head seat pocket.
During engine operation, fuel may migrate into the small gap. The fuel in the gap is generally benign when used with conventional fuel mixtures containing about 90% gasoline and 10% ethanol. However, the fuel in the gap may be more problematic when the fuel contains high percentages of ethanol, such as the E85 blend which contains 85% ethanol and 15% gasoline. Specifically, high concentrations of ethanol in the gap may enable the aluminum cylinder head seat pocket to corrode. Excessive corrosion of the cylinder head seat pocket may enable the valve seat insert to shift over time such that the valve no longer fully closes causing a loss of compression and possible overheating and damage to the valve.
The inventors herein have recognized that one source of corrosion may be a galvanic reaction as the electrically conductive ethanol acts as an electrolyte to transport ions from the aluminum cylinder head seat pocket to the valve seat insert. The valve seat insert acts as a cathode and the aluminum cylinder head seat pocket acts as an anode in the reaction. As ions are conducted from the anode, the anode material corrodes and the cathode material remains substantially free of corrosion.
One approach to address the above issues includes a valve seat insert for a cylinder head seat pocket of an internal combustion engine. The valve seat insert comprises an annular body comprising a first material and including an inner surface, an outer surface opposite the inner surface, a front surface adjoining the inner and outer surfaces, and a back surface opposite the front surface adjoining the inner and outer surfaces. The front surface includes an inner circumference greater than an inner circumference of the back surface. The back surface includes a first recession. A sacrificial anode comprising a second material different from the first material and including an exposed surface may be inlaid in the first recession of the back surface of the annular body. In this manner, the sacrificial anode may be preferentially corroded instead of the aluminum cylinder head.
Furthermore, a complementary approach to address the above issues includes a method for delivering fuel in an engine. The engine may include a cylinder head including a valve seat insert including a sacrificial anode facing the cylinder head. The method comprises inducting injected electrically conductive fuel past the valve seat insert and conducting ions from the sacrificial anode via a galvanic reaction. In this way, it may be possible to substantially reduce corrosion of the cylinder head seat pocket.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.